The present invention relates to a solenoid. Such a solenoid may be used as an actuator in various applications.
A known type of solenoid comprises a coil or winding of a conductor on a ferromagnetic stator. The stator is hollow and contains a ferromagnetic armature which is movable rectilinearly inside the stator. Once sufficient electric current is supplied to the coil, the armature moves axially of the coil. A return spring is provided to return the armature to a rest position when current to the coil is interrupted.
Solenoid actuators of this type are in widespread use and generally function satisfactorily. However, in hostile environments and/or in critical applications where failsafe operation is required, problems can arise in ensuring that the armature returns to its rest position when the coil current is interrupted. For instance, if the return spring breaks, then the restoring force is lost and the armature may not return to its rest position. Also, if the armature becomes bent or if contaminants such as particles of dirt enter the gap between the armature and the stator, the armature can become locked in the actuated position and the return spring may be incapable of returning the armature to the rest position.